1. Field of the Invention
This invention relates to a process for the manufacture of a thermoplastic or cross-linked polyurethane, or a polyurethane foam, from commonly used starting materials using as a catalyst, a guanidine or thiourea having the formula: ##STR2## in which X is S or HN and n is a whole number from 2 to 6.
2. Description of the Prior Art
The manufacture of thermoplastic or cross-linked polyurethane plastics, or polyurethane foams, with widely diverse physical properties by known isocyanate-polyaddition processes from compounds having several Zerewitinoff active hydrogen atoms, such as higher molecular weight polyols and chain extenders and organic polyisocyanates using catalysts and optionally blowing agents, emulsifiers and other auxiliaries and additives has been conducted on an industrial scale for a long time. Polyurethane processes are described in monographs by J. H. Saunders and K. C. Frisch High Polymers, Volume XVI, "Polyurethanes," Parts I and II (Interscience Publishers, New York) and R. Vieweg and A. Hoechtlen, Plastics Handbook, Volume VII, Polyurethanes, Carl Hanser Publisher, Munich.
Polyurethane foams are preferably produced from liquid materials reacted either by the one-shot process or from an isocyanate group-containing prepolymer, made from a polyol and an excess of polyisocyanate, which is then cross-linked such as by reaction with chain extenders or with water and is foamed with blowing agents if the application so warrants.
Tertiary amines are suitable catalysts for the manufacture of polyurethanes, particularly polyurethane foams. These catalysts accelerate the reaction between hydroxyl groups and isocyanate groups as well as the reaction between water and isocyanates. The reaction rates of parallel reactions can be adjusted even when working according to the one-shot process. The catalyst not only determines the reaction rate but also decisively influences the physical properties of the resultant polyurethane.
Tertiary amines which do not contain active hydrogen atoms, such as triethylene diamine, N-ethylmorpholine, dimethylcyclohexylamine, pentamethyldiethylenetriamine, tetramethylbutylene diamine or bis(dimethylaminoethyl)ether, are not incorporated into the polyurethane plastics so that they may migrate as time goes by. This migration can result in undesirable side effects such as odor or skin irritation, and the accelerated hydrolytic decomposition of the completed foam. Also, the ongoing reactions are not always accelerated to such a degree as is required for an optimum reaction with respect to processability of the starting material and to the final properties of the polyurethanes.
Because tertiary amines which do contain reactive hydrogen atoms, such as 2-N,N-dialkylaminoethanols, N-alkyldiethanolamines and triethanolamines are incorporated into the polyurethanes, these amines show a faster reduction in catalytic effect threby delaying or even stopping the reaction.
High molecular weight catalysts such as tertiary amino-group containing polyether polyols are free of odor, but as a rule do not have sufficient catalytic activity.
A purpose of this invention was to develop a catalyst which does not have a bad odor or cause skin irritations, does not promote secondary reactions such as the formation of allophanate, biuret, isocyanurate and carbodiimide groups, and which guarantees the syncronous course of the polyurethane formation and the foaming process.
Surprisingly, this purpose is achieved by using a guanidine catalyst, a thiourea catalyst, and mixtures thereof for making polyurethanes, optionally in combination with organic tin compounds.